Boring of holes in rock faces can be conducted in a variety of ways. For example, explosive boring, as the name suggests, involves drilling in the rock face a central primary hole and a series of secondary holes about the primary hole. The secondary holes have a diameter suitable to receive an explosive charge, while the primary holes provides an opening in the rock towards which cracks that are formed in the rock after detonation of the explosive, can propagate. The primary hole is normally of a greater diameter than the secondary holes. Cracks that propagate from the secondary holes to the primary hole create rock chips or segments, that can be separated from the rock being bored and which are thereafter removed, leaving behind a bore hole. The size of the bore hole required determines the number of primary and secondary holes needed, while each explosive detonation can only remove a certain amount of rock, so that the above process may have to be repeated several times to form a bore hole of sufficient cross section and length. As can easily be appreciated this method of boring can be quite dangerous due to the use of explosive material, while it is also time consuming and complicated to prepare the primary and secondary holes in the rock face. Additionally detonation of the explosives is a skilful exercise, as each explosive is detonated separately and at different times, to achieve the greatest extent of crack propagation.
A different form of rock boring involves the use of roller cutters that are rotationally forced into impact with the rock to again create cracks that propagate through the rock. The roller cutters employ a plurality of cutting tips, arranged at a variety of different diameters, which are forced into engagement with the rock surface adjacent one another, so that cracks are formed by one cutting tip propagate and intersect with cracks formed by an adjacent tip, thus created a rock chip or segment that can be separated from the rock under the impact of the roller cutter. Applying immense compressive forces to the rock creates the cracks, and eventually a balancing tensile failure occurs. Boring devices of this kind are subject to extensive impact loading because the cutting tips are forced into engagement with the rock under large loads in order to generate the cracks in the rock and thus the rock boring device is required to have facility for large impact absorption. The impact absorption is provided by way of a huge absorption mass attached to the device and the mass is of such a size, that known boring devices can weigh many hundreds of tonnes, a substantial component of which is for impact absorption. As a consequence, the weight and size of these devices makes them expensive to construct and operate.